1. Field of the Invention
The invention is generally related to the mooring of floating offshore structures and more particularly to a method of setting mooring lines for floating offshore structures in deep water.
2. General Background
In the offshore drilling industry, floating structures such as tension leg platforms and deep draft floating caissons are being used in five thousand feet of water and deeper. Such structures are held in position by a plurality of mooring lines that each have one end attached to the floating structure and the opposite end attached to anchors or pilings embedded in the sea floor and spaced laterally from the floating structure. The length of each mooring line between the floating structure and the anchor may be twenty thousand feet or more, with the mooring line having a diameter of four to five inches. Since such lines are not normally manufactured in such lengths, connectors must be used to attach several lines together. These connectors are a larger diameter than the line and are not flexible. As a result, a traction or drum winch is unable to maintain tension on the line without damaging the connectors. The use of a linear winch alone, which uses coaxially aligned grippers that open and close in an alternating fashion to allow the passage of these connectors present the problem of being much slower than traction winches. This presents a need for a time saving means of setting out long mooring lines having connectors that can not be passed around a traction winch while maintaining tension on the line.